Such combined systems have previously been disclosed in French patent specification no: FR 2596893 and International patent specification no. WO 95/20242.
In FR 2596863, a plane mirror is placed it an electron microscope, at 45° to its axis. For Raman spectroscopy, an illuminating laser beam passes through a window in the electron microscope housing. The 45° mirror reflects the laser beam towards a sample, along the axis of the electron microscope. The beam is focussed to a spot on the sample by a Cassegrain objective. Raman scattered light is collected by the Cassegrain objective and reflected by the mirror through the window to a spectrometer. For electron microscopy, the electron beam irradiates the sample through central apertures in the 45° mirror and the Cassegrain objective. Simultaneous examination of the sample by both electron microscopy and Raman spectroscopy is therefore possible, and the Cassegrain objective has a wide collection angle for efficient collection of the very weak Raman scattered light. However, in practice it is difficult to mount both this objective and the 45° mirror in the restricted space available in the sample chamber of a commercial electron microscope. FR 2596863 therefore mounts them within the electron lens system.
WO 95/20242 points out various problems of that arrangement. It proposes to overcome these problems by mounting the sample on a displaceable mount. The optical system for the Raman spectroscopy is not co-axial with the electron microscope, and the sample is moved on its mount from one to the other. However, this makes simultaneous examination by the Raman and electron microscope systems impossible. It also requires the mount to be an expensive precision stage in order to move the sample precisely between the respective analysis points of the electron system and the optical system.
A book “Raman Microscopy: Developments and Applications”, edited by George Turrell et al, Academic Press Limited, 1996, Chapter 5, pages 201-220, suggests on pages 215-216 that a parabolic mirror can be used in place of a Cassegrain objective and 45° plane mirror. This is mechanically simpler, and can be mounted within the sample chamber of the electron microscope. For Raman spectroscopy, laser light is injected transversely to the axis of the electron beam. The parabolic mirror reflects it through 90°, coaxial with the electron beam, and focuses it to a spot on the sample. The electron beam again passes through a central aperture in the parabolic mirror. The parabolic mirror collects Raman and other scattered light from its focal point, and passes it back along the transverse path out of the sample chamber of the electron microscope.
However, when such a mirror is not in use, it tends to hinder other analytical techniques, such as x-ray spectrometry of the x-rays produced by the electron bombardment of the sample. Furthermore, when the mirror is placed in the sample chamber it must be correctly aligned. Not only must the central aperture be aligned with the electron beam, but also the optical focus of the mirror must be relocated at the same point on the sample, relative to the electron beam.
It is desirable to have precise and repeatable positioning of the mirror with respect to both the analytical axis and an optical system positioned along the optical axis.
Furthermore, as an analysis system such as a scanning electron microscope may operate under ultra high vacuum it is preferable for adjustment of the mirror in both the operative and inoperative positions to be possible external to the vacuum.
One aspect of the present invention provides an adapter for performing an optical analysis (e.g. by spectroscopy) of a sample mounted in a sample chamber of another analytical apparatus (such as an electron microscope), said analytical apparatus having an analytical axis and projecting an analysis beam generally along said analytical axis towards a sample, the adapter comprising:                a mirror located so as to receive an input light beam (e.g. a laser beam) along an axis generally transverse to said analytical axis, said mirror directing said input light beam generally along the analytical axis towards the sample, and collecting the scattered light received from the sample and directing said scattered light generally along the transverse axis,        wherein said mirror is movable between an operative position on said analytical axis and an inoperative position away from said analytical axis.        
Preferably, an optical system is provided for processing the input light beam and the scattered light, said optical system being movable together with the mirror as the mirror moves between the operative and inoperative positions. Preferably the optical system includes one or more filters for rejecting light having the wavelength of the input light beam from said scattered light.
Preferably the mirror is concave, in order to focus the input laser beam onto the sample and collimate said scattered light.
Preferably the concave mirror is a paraboloid mirror, in order to focus a spot (which can be diffraction limited) onto the sample from a collimated input light beam, and in order to produce a collimated output light beam of said scattered light collected from said spot. The optical system may output the scattered light to a spectroscopy system, to analyse the spectrum of the scattered light collected from the spot.
A second aspect of the present invention relates to a light injection and rejection arrangement for a spectroscopy system.
A spectroscopy system is known from European Patent Application No. EP 543578, in which exciting laser light is injected into an optical path and directed towards a sample by a dichroic filter. The dichroic filter is preferably a holographic filter at a low angle of incidence, e.g. 10° to the optical path. Light which is epi-scattered from the sample returns back along the optical path to the dichroic filter. Desired inelastically scattered light (e.g. Raman) passes through the filter to a spectrometer system, while undesired elastically scattered (Rayleigh) light is rejected by the filter.
The filter in such an arrangement must be designed to reflect the wavelength of the laser used. This ensures that it can reflect the incoming laser light towards the sample, and can reject the elastically scattered light having the same wavelength as the laser.
It is often desirable to be able to change the laser, in order to use a different excitation wavelength.
With the arrangement of EP 543578, the means that the filter must also be changed to match the new wavelength. Unless special measures are provided for accurate positioning of the filters, this can entail an awkward and time-consuming job of realigning the system with the new filter.
In its second aspect, the present invention provides a light injection and rejection arrangement for a spectroscopy system, for use with at least two different monochromatic light inputs (such as lasers), comprising:                an optical path extending between a sample to be analysed and a spectroscopy system for performing such analysis,        first and second inputs for receiving respective first and second excitation beams at respective first and second wavelengths,        a first filter located in the optical path, at an angle such that it directs the first input beam towards the sample, and rejects elastically scattered light received from the sample while passing inelastically scattered light for analysis towards the spectroscopy system,        a second filter located in the optical path, at an angle such that it directs the second input beam towards the sample, and rejects elastically scattered light received from the sample while passing inelastically scattered light for analysis towards the spectroscopy system,        light being received from the second filter which has been rejected from the optical path by the second filter when the sample is excited at the first wavelength, said light therefore representing desired inelastically scattered light, and        said rejected but desired inelastically scattered light either being recombined with other inelastically scattered light, or being detected separately.        
A third aspect of the present invention provides an adapter for performing optical analysis of a sample mounted in a sample chamber of another analytical apparatus, said analytical apparatus having an analytical axis and projecting an analysis beam generally along said analytical axis towards a sample;                the adaptor comprising an optical element located so as to collect scattered or generated light received from the sample and directing said light generally along an optical axis at an angle to the analytical axis;        wherein said optical element is adjustable between an operative position on said analytical axis and an inoperative position away from said analytical axis;        characterised in that the operative position is defined by an adjustable mount which restrains movement of the optical element in six degrees of freedom.        
Preferably the adjustable mount is kinematic.
Preferably there is reduced pressure inside the sample chamber, wherein said reduced pressure is used to bias the optical element towards the operative position.
Preferably the optical element also receives an input light beam along the optical axis, said optical element directing said input light beam towards the sample.
Preferably the optical element is a mirror. It may alternatively be a fibre optic light collection element.
Preferably the optical axis is generally transverse to the analytical axis.
The inoperative position may be defined by a second mount which constrains movement of the optical element in six degrees of freedom. This second mount may also be adjustable.
A fourth aspect of the present invention provides an adapter for performing optical analysis of a sample mounted in a sample chamber of another analytical apparatus, said analytical apparatus having an analytical axis and projecting an analysis beam generally along said analytical axis towards a sample;                the adapter comprising a first optical element having a first focal plane, the first optical element being located so as to collect scattered or generated light received from the sample and directing said light generally along an optical axis at an angle to the analytical axis;        wherein said optical element is adjustable between an operative position on said analytical axis and an inoperative position away from said analytical axis;        wherein a second optical element, having a second focal plane, is provided in a fixed relationship the first optical element to direct light directed along the optical axis by the first optical element towards an optical analyser;        characterised in that the first and second optical elements are arranged such that when the first optical element is in the operative position, their focal planes are parallel with the direction of movement of the first optical element;        such that there is at least part compensation for inaccuracies in the positioning of the first optical element in tis operative position.        
Preferably a location mount is provided to define the position of the first optical element in its operative position; and wherein when the first optical element is in the operative position, the ratio of the focal length of the first optical element to the focal length of the second optical element is inverse to the ratio of the distance along the optical path between the focal point of the first optical element and the location mount to the distance along the optical path between the focal point of the second optical element and the location mount.
Preferably the focal lengths of the first and second optical elements are equal and wherein the distance along the optical path between the focal point of the first optical element and the location mount is equal to the distance along the optical path between the focal point of the second optical element and the location mount when the first optical element is in the operative position.
Preferably the first and second optical elements comprise parabolic mirrors.
A fifth aspect of the present invention provides an adapter for performing optical analysis of a sample mounted in a sample chamber of another analytical apparatus, said analytical apparatus projecting an analysis beam towards a sample;                the adapter comprising an optical element located so as to collect scattered or generated light received from the sample and directing said light generally along an optical axis and to the optical analysis means;        characterised in that the optical element is a parabolic mirror;        wherein at least one mirror is provided to align light reflected by the parabolic mirror with the optical, analysis means, the position of the at least one mirror being adjustable;        and wherein distortion at the optical analysis means is corrected using image, processing software.        
Preferably a second parabolic mirror is located between said parabolic mirror and the optical analysis means, wherein the two parabolic mirrors are arranged in an aberration-cancelling orientation. A further two parabolic mirrors may be located between, said parabolic mirror and the optical analysis means, wherein the four parabolic mirrors are arranged in an aberration-cancelling orientation.
Reference should be made to U.S. Pat. No. 5,446,970 for a discussion of one meaning of the terms “kinematic”, “kinematically” and like terms, as used in this specification. These terms encompass not only kinematic supports in which point contacts are provided between the respective pairs of elements on the carrying and receiving members, but also semi- or quasi-kinematic supports, in which there are small areas or lines of contact between the respective elements.